Aromatic polyimide and polybenzoxazole membranes for the fractionation of aromatic/aliphatic hydrocarbons by pervaporation

A series of aromatic polyimides and polybenzoxazoles was synthesized and tested as membrane materials for separation of aromatic/aliphatic mixtures by pervaporation. Homo- and random copolyimides were synthesized by a two-step polycondensation of a total of 6 diamines and 4 dianhydrides. Polybenzoxazoles and poly(benzoxazole-co-imide)s were prepared by the thermal rearrangement of ortho-functionalized polyimide films. Pervaporation experiments were conducted at 80 °C with either toluene/n-heptane or benzene/n-heptane mixtures as feed streams. All polymers were selective towards the aromatic hydrocarbon, whose permeability could be changed by approximately 4 orders of magnitude depending on the chemical structure of the diamine. Pure-liquid sorption experiments at 25 °C revealed that these large changes in hydrocarbon permeability were mainly caused by changes in the diffusion coefficient. The performance of the polymers was compared with previous results reported for other polymers, as well as with the performance of a commercial polyimide (Matrimid®).

Figure optionsDownload high-quality image (116 K)Download as PowerPoint slideHighlights
► Homo- and copolyimides were synthesized using 6 diamines and 4 dianhydrides.
► Dense polyimide and TR polymer films were tested as pervaporation membranes.
► All polymers were selective towards the aromatic hydrocarbon.
► Hydrocarbon permeability spanned 4 orders of magnitude depending on the diamine.
► Changes in diffusivity are the main reason for large changes in permeability.